The flipped classroom is gaining more attention than ever before due to the pandemic of the COVID-19, by which online learning becomes a must in many countries and territories all over the world. The flipped model is a combination of online and face-to-face learning in which students watch instructional videos and do certain comprehension tasks at home prior to in-class lessons. To our knowledge, few studies have been conducted to explore the impact of flipped classrooms for teaching English reading skills in the high school context. The current experimental study has been conducted in a high school in the Mekong Delta with 52 students at Grade 11 in a high school in the Mekong Delta of Vietnam. Students were assigned to watch videos of instructions for 6 reading lessons in the English Grade 11 Textbook for 10 weeks. Learners’ reading comprehension performance and attitudes are compared between the control group and the experimental group. The findings reveal some interesting implications for Vietnamese teachers teaching English at high school